The invention relates to the use of organometallic compounds containing aluminum, gallium or indium as metals for the production of thin films or epitaxial layers by gas-phase deposition.
The deposition of such layers consisting either of pure elements of group III or of combinations with other elements, such as, for example, gallium arsenide, indium phosphide or gallium phosphide, can be used to produce electronic and optoelectronic switching elements, compound semiconductors and lasers. Such layers are deposited from the gas phase.
The properties of such films depend on the deposition conditions and on the chemical composition of the deposited film.
All the known methods, such as the metal-organic chemical vapor deposition method (MOCVD), the photo-metal-organic vapor phase method (photo-MOVP) in which the substances are decomposed by UV radiation, the laser chemical vapor deposition (laser CVD) method or the metal-organic magnetron sputtering method (MOMS) are suitable for the deposition from the gas phase. The advantages over other methods are a controllable layer growth, a precise doping control, and also simple handling and ease of production owing to the normal or low-pressure conditions.
In the MOCVD method, organometallic compounds are used which decompose at a temperature below 1100.degree. C. with the deposition of the metal. Typical pieces of equipment which are at present used for MOCVD consist of a "bubbler" with a feed for the organometallic components, a reaction chamber which contains the substrate to be coated, and also a source for a carrier gas which should be inert with respect to the organometallic component. The "bubbler" is kept at a constant, relatively low temperature which is preferably above the melting point of the organometallic compound but far below the decomposition temperature. The reaction or decomposition chamber preferably has a very much higher temperature, which is below 1100.degree. C., at which the organometallic compound completely decomposes and the metal is deposited. The organometallic compound is converted to the vapor state by the carrier gas and is channelled into the decomposition chamber with the carrier gas. The mass flowrate of the vapor can readily be controlled and, consequently, a controlled growth of the thin layers is also possible.
Hitherto metal alkyls such as, for example, trimethylgallium, trimethylaluminum or trimethylindium have chiefly been used for gas-phase deposition. However, these compounds are extremely sensitive to air, spontaneously inflammable and, in some cases, unstable even at room temperature. Costly precautionary measures are therefore necessary for the production, transport, storage and use of said compounds. A few, somewhat more stable adducts of the metal alkyls with lewis bases, such as, for example, trimethylamine and triphenylphosphine, are known (for example, described in GB 2,123,422, EP-A-108,469 or EP-A-176,537), but these are only of limited suitability for gas-phase deposition because of the low vapor pressure.